This project is being submitted in two separate grant proposals to facilitate administration of funds. Grant No. AM25472 will be submitted by Robert Armstrong, Oral Roberts University, School of Medicine. This proposal has two main objectives: a) to determine the manner in which muscles and populations of fibers within muscles are recruited during locomotion: 1) as animals increase speed and change gaits; and 2) as animals use their muscles for different tasks, i.e. positive mechanical work and elastic storage of energy. b) to investigate the contribution of skeletal muscle to total resting metabolism. We have been using the following techniques: EMG's synchronized with high speed movies of running animals to determine the activity and length changes of active muscles; glycogen loss from muscle fibers to determine the cross-sectional area of active muscles, populations of active fibers, and the power of active muscles; length changes of tendons as a means of measuring force exerted by a muscle during locomotion; blood flow to muscle groups together with oxygen extraction from the blood to measure their oxygen consumption and 24 hour metabolic rates of mammals whose resting metabolism and maximum aerobic metabolism vary by approximately 5-fold. In the coming year we will begin studies of the energetics and mechanics of isolated muscles, using temperature as a variable to alter intrinsic velocity of the muscle.